string querySaveFile = String.Format("select t1.id, t1.{0}, t2.{1} " +
                "from {2}.dbo.{3} t1 " +
                "left join {4}.dbo.{5} t2 on t1.id = t2.{6} " +
                "where t1.id = {7}",
                 ConnectionString.DoVarchar, colNameImageCmb.Text, ConnectionString.InitialCatalog, ConnectionString.TableNameText,initialCatalogTxb.Text, tableNameCmb.Text, fieldCommunicationCmb.Text, fileId);
command = new SqlCommand(querySaveFile, conn);
reader = command.ExecuteReader();
dt.Load(reader);
reader.Close();
foreach (var item in dt.Select())
{
   string fileName = (string)item[ConnectionString.DoVarchar];
   String newFileName = Path.GetInvalidPathChars().Aggregate(fileName, (current, invalid_char) => current.Replace("'", "_"));
    byte[] fileContent = (byte[])item[colNameImageCmb.Text];;


    string queryLoad = "UPDATE @table_name SET @filestream = @file_content, @datetime = (GetDate()) where \"id\" = @file_id";                                      
    command = new SqlCommand(queryLoad, conn);
    command.Parameters.Add("@table_name", SqlDbType.VarChar, ConnectionString.TableNameText.Length).Value = ConnectionString.TableNameText;
    command.Parameters.Add("@filestream", SqlDbType.VarChar, ConnectionString.Filestream.Length).Value = ConnectionString.Filestream;                                      
    command.Parameters.Add("@datetime", SqlDbType.VarChar, ConnectionString.Datetime.Length).Value = ConnectionString.Datetime;
    command.Parameters.Add("@file_content", SqlDbType.VarBinary, fileContent.Length).Value = fileContent;
    command.Parameters.Add("@file_id", SqlDbType.Int).Value = fileId;
    ommand.ExecuteNonQuery();                                            
  }
}

String or binary data would be truncated. The statement has been terminated

private void TransferFiles()
        {
            int fileId = 0;
            using (SqlConnection conn = new SqlConnection(ConnectionString.Value))
            {
                try
                {
                    conn.Open();
                    string fullPath = System.Reflection.Assembly.GetAssembly(typeof(Form1)).Location;                    
                    string theDirectory = Path.GetDirectoryName(fullPath);                                             
                    DataTable dt = new DataTable();
                    DataTable dt2 = new DataTable();
                    string queryOpen = String.Format("select top {7} t1.id, t1.{0}, t2.{1} " +
                                                     "from {2}.dbo.{3} t1 " +
                                                    "left join {4}.dbo.{5} t2 on t1.id = t2.{6} " +
                                                     "where t2.{1} is not null and t1.{8} is null",
                                                     ConnectionString.DoVarchar, colNameImageCmb.Text, ConnectionString.InitialCatalog, ConnectionString.TableNameText,  initialCatalogTxb.Text, tableNameCmb.Text, fieldCommunicationCmb.Text, numericNumberOfLines.Value, ConnectionString.Datetime);                    
                    if (!String.IsNullOrEmpty(tableNameCmb.Text) && !String.IsNullOrEmpty(colNameImageCmb.Text) && !String.IsNullOrEmpty(fieldCommunicationCmb.Text))
                    {
                        SqlCommand command = new SqlCommand(queryOpen, conn);
                        SqlDataReader reader = command.ExecuteReader();
                        dt.Load(reader);
                        reader.Close();                       
                        if (dt.Rows.Count != 0)                                                                     
                        {
                            foreach (var item in dt.Select())
                            {
                                fileId = (int)item["id"];                                
                                string fileName = (string)item[ConnectionString.DoVarchar];
                                byte[] fileContent = (byte[])item[colNameImageCmb.Text];

                                    using (FileStream fs = new FileStream(newFileName, FileMode.OpenOrCreate))
                                    {
                                        fs.Write(fileContent, 0, fileContent.Length);
                                    }
                                    
                                    string queryLoad = "UPDATE ETA_EL_DOC SET @filestream = @file_content, @datetime = (GetDate()) where \"id\" = @file_id";
                                    command = new SqlCommand(queryLoad, conn);
                                    command.Parameters.Add("@filestream", SqlDbType.VarChar, 1000).Value = ConnectionString.Filestream;
                                    command.Parameters.Add("@datetime", SqlDbType.VarChar, 1000).Value = ConnectionString.Datetime;
                                    command.Parameters.Add("@file_content", SqlDbType.VarBinary, fileContent.Length).Value = fileContent;
                                    command.Parameters.Add("@file_id", SqlDbType.Int).Value = fileId;
                                    command.ExecuteNonQuery();
                                  
                                    File.Delete(fileName);                                                                       
                                }
                            }
                            MessageBox.Show("Копирование успешно завершено!");
                        }
                        else MessageBox.Show("Нет доступных данных для копирования!");
                    }
                    else
                        MessageBox.Show("Выберите все поля!");
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
            }
        }

update ETA_EL_DOC
SET fileDATA = t2.file_doc_im, data_change = (GetDate())
from permitproc.dbo.ETA_EL_DOC t1 left join permitproc2.dbo.ETA_EL_DOC t2 on t1.id = t2.id